A power conversion device that is mounted on an electric motor vehicle such as an electric vehicle (EV) and a hybrid electric vehicle (HEV) and is connected to a motor for drive has a power conversion function of converting direct-current power for motor drive supplied from a direct-current power supply into alternating-current power or converting alternating-current power generated from a motor into direct-current power for direct-current power supply charge. To realize the power conversion function, a switching element such as a metal-oxide-semiconductor field-effect transistor (MOSFET) and an insulated gate bipolar transistor (IGBT) is generally used in the power conversion device. If a voltage more than a predetermined withstand voltage is applied, the switching element may cause withstand voltage breakdown and may be damaged. For this reason, it is necessary to cause an application voltage to be not more than the withstand voltage.
In a normal electric motor vehicle, to use power efficiently, the direct-current power supply is charged by compulsorily rotating a motor at the time of braking or descending a slope, causing the motor to function as a generator, and generating a regenerative voltage (counter electromotive force). However, when a rotation number of the motor increases, a large regenerative voltage is generated. For this reason, the regenerative voltage is more than the withstand voltage, so that the switching element may cause the withstand voltage breakdown. Therefore, to prevent the withstand voltage breakdown, a mechanism for suppressing an overvoltage is provided in the power conversion device according to the related art.
For example, PTL 1 suggests a method of turning on a switching element according to a rotation position of a motor at the time of generating an overvoltage, under control of a CPU, connecting a plurality of phases of the motor in series, and suppressing the overvoltage, in a motor control device to control the motor.
In addition, PTL 2 describes a method of controlling a switching element of an inverter by an inverter control unit, such that a regenerative voltage input from the inverter to a direct-current power supply is detected and at least one of opening and short-circuiting between a motor drive device and a motor is performed on the basis of a detection result thereof.